Printing telegraph system



R. G. GRIFFITH PRNTING TELEGRAPH SYSTEM Nov. 13, 195] 12 Sheets-Sheet lFiled May 25, 1949 Invenlor EES@ .Q x

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Nov. 13, 1951 R. G. GRIFFITH PRINTING TELEGRAPH SYSTEM.

l2 sheets-'sheet 2 Filed May 25, 1949 Nov. 13, 1951 R. G. GRIFFITHPRINTING TELEGRAPH SYSTEM 5 12 Sheets-Sheet 3 Filed May 23, 1949 l (E: MAttorney R. G. GRIFFITH PRINTING TELEGRAPH SYSTEM Nov. 1 3, 1951 FiledMay.A 23, 1949 12 Sheets-Sheet L Attorney In erzor BWM Aww R. G.GRIFFITH PRINTING TELEGRAPH SYSTEM Nov. 13, 1951 12 Sheets-Sheet 5 FiledMay 23, 1949 Inven 0l' l2 Sheets-Sheet 6 -I-/OV R. G. G RIFFITH PRINTINGTELEGRAPH SYSTEM Inventor F/as Nov. 13, 1951 Filed May 23, 1949 nnAAn"nu" Nov. 13, 1951 R. G. GRIFFITH PRINTING TELEGRAPH SYSTEM 12Sheebs-Sheet 7 Filed May 23, 1949 Invenior N0V- 13, 1951 R. G. GRIFFITHPRINTING TELEGRAPH SYSTEM 12 Sheets-Sheet 8 Filed May 23, 1949 InventorE? Y mg W M m.

M/11" Attorney l2 Sheets-Sheet 9 N0V- 13, 1951 v R. G. GRIFFITH PRINTINGTELEGRAPH SYSTEM Filed May 25, 1949 Nov. 13; 1951 R. G. GRIFFITHPRINTING TELEGRAPH SYSTEM 12 Sheets-Sheet 10 Filed May 23. 1949 InvenlorJW Attorney R. G. GRIFFITH PRINTING TELEGRAPH SYSTEM Nov. 13, 1951 l2Sheets-Sheet l1 Filed May 23, 1949 r i t Qwm,

Inventor mld BWL/7% m Attorney 12 Shets-Sheet 12 Nov. 13, 1951 R. G.GRIFFITH PRINTING TELEGRAPH SYSTEM Filed May 25, 1349 verior 4 ,Jim/VfAtiorney tive-unit equal length code and the signals may be recorded andprinted on a standard teleprinter. A pair of commutators or distributorsare then employed both driven in step with a distributor for thetransmitted signal units. One commutator transmits release pulses forthe tape transmitter or transmitters to enable the transmitter to startat the required time to transmit the signals character by character andthe other commutator provides a short interval of selection or samplingfor each signal unit. The latter commutator has for each channel, abrush which collects the sample from the tape transmitter relay at themiddle of each signal unit and which is connected to a neighbouringbrush which passes the sample of the signal to the code convertingapparatus allocated to the channel in question.

A light chopper disc and selecting pulse dis-V tributor are also drivento apply a first selecting pulse to the converting apparatus of thechannel just before the sample of the signal unit is taken and a secondselecting pulse just after the sample is taken. The chopper is aconstantly driven disc formed with uniformly spaced slits arranged topass light from a lamp to a photo-electric cell in sequence; the currentpulses in the cell are amplifled and applied to the ring of theselecting pulse distributor which passes the pulses to brushes connectedto the converting apparatus ofthe single channel or to the apparatus ofone of the channels.

- The commutators or distributors and the light chopper are driven instep at appropriate speeds as will be explained more fully later, forexample, from a synchronous electric motor controlled from a harmonic ofa standard tuning fork.

The code converting apparatus for one channel may conveniently comprisea double triode coupled as a flip-nop, the rst grid of which receivesthe samples of the signal units. (In Fig. 3 of the drawing, the rst gridand anode are in the right hand half of tube V1.) If a signal unit ispositive, the first anode of the iiip-flop triode is made conductive andthe second anode swung to positive voltage. If the signal unit isnegative, the flip-nop is changed over and its rst anode becomespositive. Its second anode is connected directly to both anodes of asecond ip-iiop connected double triode and its first anode is connecteddirectly to both anodes of a third nip-nop connected double triode. Theiirst selecting pulses of the channel from the selecting pulsedistributor are applied to the rst grids of both the second and thirdhip-flop triodes and the second selecting pulses are applied to thesecond grids of both the second and third nip-flop triodes. The rstcathode of the second :flip-flop triode is connected to the secondcathode of the third flip-flop triode and both are connected to the rstgrid of a main output flip-nop double triode preferably through a diodewhile the second cathode of the second ilip-op triode and the rstcathode of the third '.tlip-ilop triode are similarly connected to thesecond grid of the main output flip-op triode.

With this system, the conversion of normal equal length signal unitsinto transit code signals takes place as follows:

If a positive signal unit is being sent by the tape transmitter, thefirst grid of the rst iiipilop triode receives a positive pulse and itssecond anode becomes positive and remains positive and keeps both anodesof the second flip-flop valve positive until a negative signal unit issent. The

rst selecting pulse is applied to the iirst grids of the second andthird flip-flop triodes. Therefore, the rst anode of the second nip-flopvalve only becomes conductive and a pulse iiows through it to the firstgrid of the main output iiip-op triode so that its rst anode becomesconductive which is the condition of marking modulation. The secondselecting pulse then passes to the second grids of both the second andthird ip-iiop triodes so that the second anode of the second nip-flopvalve only is now conductive and a pulse flows through it to the secondgrid of the main output flip-flop triode so that the second anode ofthat triode becomes conductive and that is the condition of spacingmodulation. Thus a positive five-unit signal unit has been translatedinto a transit from marking to spacing modulation.

If, on thevother hand, a negative signal is being sent, the iirst anodeof the rst flip-flop triode becomes positive and renders both anodes ofthe third flip-flop valve positive and they remain positive until thenext positive signal unit is sent. Then on the arrival of the iirstselecting pulse,

' the rst anode of the third nip-flop valve conducts and passes apositive pulse to the second grid of the main output flip-nop valvewhich accordingly assumes the condition of spacing modulation. On thearrival of the second selecting pulse, the second anode of the thirdflip-iop triode conducts and passes a positive pulse to the first gridof the main output flip-flop valve which thus assumes the condition ofmarking modulation. Thus a negative five-unit signal unit is convertedinto a transit from spacing modulation to marking modulation. The mainoutput flip-flop triode is preferably coupled to an amplifying stage andthe output signals to be applied to the transmitting aerial appearacross a cathode resistance in the output circuit of this stage.

The necessary receiving arrangements depend on the fact that a positivesignal unit consists of a marking condition with a transit to a spacingcondition and a negative signal unit consists of a spacing conditionwith a transit to a marking condition. l'n the preferred case, themarking and spacing conditions each occupy 50 per cent of a signal unit.Thus, a positive signal unit always has a mark as its rst half and anegative unit has a space as its iirst half; therefore, if the signalunits are explored or a selection made during the first half of eachunit and preferably at the mid point of that half, the positive andnegative units are distinguished by selecting, at those times, marks andspaces respectively. This can conveniently be arranged by applying thesignals to electron valves and impressing on their grids a shortselection pulse at the times mentioned, whereupon one valve will conductfor the positive signal unit and the other for a negative signal unit.Then, if the current in each valve is arranged to operate a suitableform of relay, that relay will indicate positive and negative signalunits which have thus been reconverted into signal units of the primarycode. This relay may consist of two valves or a double valve connectedto have two conditions of stability so that one or other of the valvesis made conductive on reception of a positive or negative signal unitand remains conductive until the arrival of the next selection pulse.The signal units, therefore, appear at the anodes of that Valve orvalves and can be utilised to control the operation of a channel outputrelay.

admetsceiving valves: are controlledby a second selectief-1'A pui-'selini eachsignal uni-tl which occursl preferably at the middleofthe-*secondx haii'- oi each'` signalA arefcross-connectediwithlrespectto. the: ano'des oi th'eiiip-iiop valve et the signal selector circuit;

The-result oft this-is that,` a-tl-th'etime ofthe-.sechondpul'se ea'ch-sig-nal unit, ifi the signal. is not.. miiltilatedythe2 second'selection pulse renders;

thatariode'oithe-comparatornin-flop valve condietive which doesn'ot'receiv'cl a voltagei from. the. signal-s On -theothenliandfifvthasignahis mu.- tilated andc'onsists-'of a marlsin'gcondition. follevied! by a marking .condition-.Orla spacing. condi.-tionfollow'ed-by aspacing condition. when the.

second. selectionpulse. arrives; the voltage is.ap-

pliedto the anode-.ot that .Vallve corresponding. to. the grid which`is. made conductive;. then one or. other anode passesA current whichisrrectie'd. inl al pair. of valves or a ldouble valveandpasses an im.pinsetoione` grid. oan errorindicatorvalve. ThatA valve then conductscurrent which passesV it through the. winding of. an'` error lindicating relay andthus indicates the error. This relay also/has aresetting.- Winding-'connectedto..a.1second anode ofthe-.errorin'dicator valve which is renderedqconductive by an. error.reset double valve. or pair of valves connectedin. thesame wayasthecomparat'orfiiip-lop valve-except th'atits grids.` arecrossconnected with a respect tol those. of thelatter valve. Thusv theerror reset valvepasses` current. upon the reception of. acorrectsignal.andrenders thesecondanode o"` the errorindicatorvalvecomductive. s that current passes through. the reset.

winding. ofthe error' indicatorrelay` Thesen circuits are: repeated each.channel so. that in'a four channelmultiplex. systeme at each. cyclethere are four rst selection pulses`..inter spersed -with `foursecond.:` selection. pulsesi- These'.

pulses are preferably set up` by. asynchronously drivenshutter disc.with narrow iadialslotsrmovedL between.l alamp and a photofelectriccell; impulses so-generat'ed are distributedat `the prop'- er7 times tothe selector and.: comparator. circuits; of the four channels through acommutator with eight brushes.. The shutter Vdisc-is. driven by asynchronous motor fed'4 through a 50eycle per second multi-vibratorcircuit locked to .a harmonie-oii ai standard tuni-ngl` fork-and.. iskept .in vsync-hronism with'. the incomingsignals.- Thismay-be eiected.by? dierentiating and rectif'ying the'sig-y nais andappiyi'ngtheresulting-short pulses to' the gr-id oa gated valve, theanode oi which receives volts through` brushes onthe. commutatorreferred toabove, at one time in each cycle. These pulses arei compared.withsquare topped Waves obtained from.- a chopper disc driven by thesynchronousmo't'or which drives4 the shutter disc. The chopper disccontrols iightl passing to another photo-electricceli, the emission fromwhich is ampliedfand applied-to key a pair of.' fliplopvalveswhich thusproduce a square topped voltage wave at' their ainode's. TheseVoltage'sare applied to the anodes ofi :iw-further' pair oiv'alv'eswhose grids receive thev pulses derived from. tl'jie` signalsalready-vdescribed. these.A pulses arrivel exactly' at the time of change-overofthe Ysrmare topped waves, the lastmentionedtwo valves pass current' butif' the- The.

oven'. onefofi the: valves has voitson. its anode and passesIwlfralr,mayfxbes called. an Iadvancing;orl ifea'- tarding currentimpulse. Theself-aref'respectively? storedaincondensers .whichultimatelytrip, one or other of two` gasldischarge; valves; the anodecurr rentsofi these.. valves energise;v relays which: re-

verse .adirect current shuntV phasing motorrwhich..`

turns'fthestatorci the synchron-ous'. motor driv ing the shutterVdisc',` forwards` or backwards; to bring it into:synchronisn'i.Y

The channel: output signals are synchronous*l signals an'dmay beconvertedcintostart-stop siggV nais by ai channel distributor which mayalso pre.-

venti the passing-onor av character: if an error'l has' occurred` in oneof: its signalunits. The-comv mutator consists of. two parts. brusheswhich, .thrcughisegmenta,store the re-u ceived signal units in a.series-.of condensers. The:-

other part of thezcommutator, through other segl ments suitably spaced,sends a' start signal fol lowed by the units. ofv he precedingcharacter-f which are followed by the stop signal. This corn--ymutator'sends on. to the line-relay the signalszof a given characterjustbeiore the. signalsofy the next; characters are stored' in thecondensers.

Theerror indicatingrelay is arranged, on thev occurrence of an. error,to energise an errori re'- setting relay and a polarised relay. When thebrushes of the-second part of the commutatorV reach an error` indicatingsegment after the-.stop signal hasv been sent, thepolarised relay openscontacts and thus prevents the signals of thev character from being sentto the line relay?.

When, however, a signal which isnot mutilatedr arrives, the second part'of the commutator, aftersending the stop signal, makes contact with an+other or reset segment so that current issent to.` the pclarised relayto reset the latter" and reestablish normal Working;

In order to explain the invention more fully,

a system will .be considered in greater detail, by?

way of example, of. a four-channel mutliplex tele-Y graph especiallysuited for used on radio chan-- nels and the transmitter and receiverwill nowf be described with reference to the accoiripanyingA drawings inwhich:

Figure 1 is a block diagram showing, the trans.;-T mitting arrangements;

Figure 2 is a circuit diagram of the tape transmitter and itsconnections to the outputrelay in the rst or A channel;

Figure 3 is a circuit diagram illustratingcthetiming of thedistributors. and showing in detail the Av channel converter and keyerand the main outputrelay; while Figure 4 is a diagram illustrating thetiming ofthe transmitter components;

Figure 5 is a block diagram showingV in gen-P eral the components of thereceiver;

Figure 6 is` a circuit diagram of the main rg!-T ceiving relay;

Figure 7 is a circuit. diagram of the main parts of the receiverincluding the channel selector and comparator' and the components forthe-first'. and second signal selection, signal comparison;

Figure s is a circuit diagram of the radio con ditions indicator to beVused in conjunctionv with Figure '7;

Figure 9 is a diagram illustrating the timing of the main receivingapparatus;

Figure 10 is' circuit diagram Showing the method of controlling thephase o f the receivingl unit by means of the received signals; f

Figure 11 is a timing diagram related ure'lO-i c Figure 121s a' circuit'diagram of the'untx for t0 Fig- The first, has'Y converting synchronousfive-unit signals into start-stop signals; and

Figure 13 is a modification of Figure 12 showing connections forrepetition working.

Referring particularly to Figure 1, there is a transmitter AT, BT, CT,DT for each of the four channels and, in this example, each transmittercomprises a set of contactors controlled by paper tape perforatedaccording to the 5-unit code and connected to an output relay at whichthe positive and negative signal units appear in the 5unit code. Theoutputs of the four channels are supplied by conductors I, 2, 3, 4 tobrushes SCI, SC2, SC3, SC4 of a commutator SC having ten equally spacedcontact segments and, by means of the commutator, the channel signalsare distributed in sequence to four brushes SCA, SCB, SCC, SCD with atiming which will be described later and by way of four conductors 5, 6,1, 8 to four channel converters and keyers AK, BK, CK and DK.

Associated with the commutator SC and rotated at the same speed is arelease commutator RC the function of which is to earth through aconnection 9, four brushes RCA, RCB, RCC and RCD with a timing whichwill be described more fully below so as to send start pulses throughconductors I0, II, I2 and I3 to release the respective tape transmittersof the four channels.

There is also a continuously driven light beam i chopper or interruptordisc LC provided with thirty-two equally spaced slits I4 which permitlight from a lamp L to pass for succeeding short intervals to aphoto-cell PCI. The pulses from the photo-cell PCI are amplified in aphoto-cell ampliiier PCA and are distributed by means of a pulsedistributor PD and eight brushes PD! to PDB, to the respective channelconverters and keyers AK, BK, CK and DK with the result, as will bedescribed more fully later, that the five unit signals are convertedinto transit code signals according to the invention, which are passedby Way of decoupling diodes, to the main output relay shown as thecomponent MR which feeds the aggregate signals by way of a connection I5to a radio transmitter and aerial.

Details of the tape transmitters are illustrated in Figure 2 in theupper part of which is illustrated in detail the tape transmitter TTAfor the A channel and below, the transmitters TTB, TTC and TTD for theother three channels are shown in block form but each is an exactreplica of that shown in detail for the A channel. In the latter, thereare the ve contactors CI to C5 corresponding to the five units of acharacter and having upper contacts It which are the respective positivecontacts and lower contacts I'I which are the respective negativecontacts. The movable members are controlled by peckers or the like sothat when there is a perforation in the paper tape and the pecker passesthrough, the corresponding contactor Ci to C5 passes to its upper orpositive contact I6 and when there is no perforation, the correspondingcontactor is held on its lower or negative contact I'I. rhe

tapetransmitter also includes a transmitting distributor TS which asshown is a half-revolution distributor so that during a half revolutionof its brush mechanism B and B2, tl e v'e units of a signal set up bythe iive contactors CI to C5, are caused to be transmitted in sequenceduring the half-revolution. Thus, the distributor TS has a common ringRI engaged by the brush BI and two sets of equally spaced segments b, c,d, e and ,f -and b', c', d',- e and f', the corre- 8 .I spondingSegments of the two sets being connected together as shown. In order toprovide reasonable time for stepping the perforated tape between thereading of successive combinations, While the contactors CI, C2 areconnected directly to the segments b, c, and b', c', the settings of thecontactors C3, C4 and C5 are established on three relays havingwindings, D, E and F and the tongues IB of these relays are respectivelyconnected to the distributor segments d, d', e, e', and f, f. Thus,electrical storage of the-last three units of a character is establishedin the relays D, E and F so that immediately the brush B2 has passedover the segment c or c', the battery illustrated on the left of Figure2 as +120 v. and -120 v. is cut oi from the contactors at the contactsPI and P2 which are opened at that stage by a cam (not shown) on thespindle of the distributor TS and then the tape is stepped on so thatthe contactors CI to C5 are set up by the next combination perforated onthe tape While the brush B2 is traversing the last three segments d, e,j', or d', e', f. The tongues I8 of the relays D, E, F, then take uppositions corresponding to those of the contactors C3, C4 or C5 sincethe relays are energised positively from battery +120 v. when each ofthe contactors C3, C4 and C5 are in their upper or positive positionsand are energised negatively from battery "120 v. when those contactorsare in their lower or negative positions.

The signals set up on the segments of the distributor TS directly fromthe contactors CI and C2 and from the tongues of the relays D, E, F, areswept by the brush BI into the conductor I9 and thence to the winding ofthe input relay IRA, the other side of which is earthed at 2) and as thetransmitter operates with double current Working, the tongue 2i of therelay IRA, oil receiving a positive unit takes the upper position givingpositive voltage to the input line I passing to the code converterapparatus and when a negative unit is transmitted, the tongue 2l takesits lower position sending negative volts to the line I.

As already indicated, the transmitters TTB, TTC and TTD for the otherchannels operate in a similar way to energise the other channel inputrelays IRB, IRC and IRD which send the signals of the respectivechannels to the input lines 2, 3 and 4.

The five contactors CI to C5 are also connected respectively throughdiodes DI, D2, D3, D4 and D5 to a voltage discriminator consisting of apair of gas discharge tubes TI, T2 of the thyratron type. The diodes DIto D5 are only provided to prevent the reverse flow of current. Thetubes TI and T2 are interconnected in a wellknown Way to secure theoperation of a relay A when the voltage applied to the grid 23 of thetube TI relatively to its cathode 24 has fallen to a pre-determinedlevel. Therefore by this arrangement when all of the contactors CI to C5are in their lower positions, that is to say, in the negative position,a negative pulse passes from battery at L20 v., through the contacts PI,the back contact a of relay A, through the contactors CI to C5 and thediodes DI to D5 to the grid 23 of the tube TI. This tube is thusrendered non-conductive. Its anode potential is therefore raised,rendering the grid 26 of the tube T2 positive. The result is that thetube T2 now passes current from battery at +120 v. through the conamazes:blank-.combinationon'thezperforated tape-but :the operation'of :relay.A iremoves zbattery 120 v. from the contactors Clto C .owingtotheinter- .ruptionatthe'backicontacta' and, 'in its place, vconnectsvbattery +120 A'v through `the rfrontcontact a2 :tothe-'contactus CI toC5 so Vthat the brushes .BI and B2 of the distributor TS lWill transmitfive positive units tinstead of .the ve negative .units Lor inntheryvords, a letter :shift :combination is transmitted'zinstead `ofthe :blank combination. Thezreason'for this@ is "ith-at a blankcombination Vis fused-to indicate a telegraph mu- :tilationat thereceiving end as will appear later and itis desirable v.that the blankYcombination shouldinot-be'transmitted.sincethat combination .isset up`when vany blank'or 4unp'eriorated .tape passes through the tapetransmitter.

@The tape transmitter is-driven by an 'electric ymotor'governed to a.constantspeed 'but the tape transmitter including the sprocket feed ofthe paperftape tand `also'thedistributor TS and its cam zalreadyreferredto are normally Aheld 'at :cest :by 'a normally disengaged clutchbetween thermotortand thetransmitter. Y'The motor and the clutchzarestandardparts"andfarenot shown inthe drawings"but 1igure '2, there 'is arelease imagnet RM ."-shown zwhich is energized by the release pulsesialready referred 4to and sent Vout by LthecommutatorfRC (Figure landFigure 3). These pulses are'sent 'out along the `conductors l0, Il,l2fand lI3,'the-conductor l0 carryring'the pulses forfthe .LA channel.The .pulses passrfromtbattery +120 v. through 'the .winding of4theifrelease` magnetiRM, the Aconductor l0 :and

the commutator L'RC Ito iearth 'at i9 and, as a result, Vthe tape vfeed'and fthe idistributor "TS are released in each Acycle"ofoperation,-that is to say,^for each stepping tandire'ading of 'the perforatedtape. The rktiming of-these :pulses will beexplainedmoreifullylater inconnection with `liigures and 4, 'but it'may'be said thatthetransmitters of vthe four channels are released in sequence sothatzthe input 'relays IRA to IRD become effective in .sequence vandprovide for the .channelling of the signals. In the particular eX- ampleunderconsideration, the distributorTS is driven at approximately 202revolutions 'per'minute,'or `in other words, it makes one revolution in288"mi1lisecondsnvhich 'gives atime .o'f 32millisecondspersignalfelement or unit. .Theabrushes Bla-nd BThOWeVer,arefarrested'fat 'the end of eachchalfrevolution-that is `to fsay,*between the segments -f and blandfa'lso :between the segments f'yandb,r-but after iadwellfo Vl'zmillisecon'dsy the brushes are againreleased by the vmagnet RM. The brushes V-come tofrestvbetween segments]'and b vfand :gf .and b, the'spacing between awhich .is half that.betweenzthe .other-segments. i

The channelsig-nals having beeniapplied4 to the conductors l, 2,3and-4fas seen in'Figures lsand 2;.proceed tothecoderconvertingaapparatusshown in :greater detailin'igure' 3. -lThecodeccnverters are-control1ed` Aby a ,synchronous motor 'Sli/I, theelectrical :drivefof which isgprovided :1in a-Vgenerally :conventionalform from a'ftuni-ng forkw'IiF havingia frequency'of $500 2 cycles per`second, the tenthqharmonic zofevvhich 'is applied through :an inverterIV tov the 4synchronous motor-@SM which thus 'receives a `constantfrequency of r-.cy'cles per: second :and fruns aat ra consta-nt `speed'of` l 500 R.P.:l\'[. .The i500:frequencysupplyzderived from the .tuning`fork :or 'it'.may be from a. quart-tz crystal, is applied Vto 'thel-inverter .IV which comprisesan amplifier feeding linto la pair`o"r"1'lip'flop connectedfgasdischarge tubes havi-ng ftheirlano'decircuits tuned? byicapacity -and inductance tothe frequency of-'50cyclesv per second. The resultzis that these-tubes :change overl-from:one Vcondition of stability .to the other at afrrequency of .5(i.:persecond which is 'taken oil` iby an output "coupled to their anode.circuitsjto themotor SM. Thefiinverter `mayzhavefa relay v.operated byshort-*circuit or excessive ycurrent which `chan-ges over torcut ofz the`supply inanemergency and zcan, att-its front contacts, "close thecircuits of Warning '.lamps.

As seen diagrammatically in Figure-3, the-:motor SMlis-geared to,therfchopperldisc LC and the pulsing distributori PD: by :gearing .suchthatthe disc .LC :and Athe distributor fPD .are driven '.atffa,constanti speed. .062468.75 revolutions :per minute zorzmakeionerevolutioniin i128 milliseconds. 'The spindle di'. the disciIsCfand.distributor PDfisr'again :geared -atZFItoithe spindle `lof ythecommutatore LRC tand iS'C iso thatlvthese rotate at a constant vspeed of2187.55 `revolutions per minute fwhich lmeans that they each ymake onerevolutioniin' 320 milliseconds 4Iitivvillibe:Observed that these makeone 'frevlutioniiin a :time 'which' is equal touth'e time .thatthetransmitter distributor `TSimakes oneirevolutionplus'fits;restperiods. As already indicated,' thercommutator SC has 'ten `equallyvspaced segments :and .therefore the 'distance' ybetween Ithelfcentresuo'f successive segments #cor-:responds'to'thetimethatfthebrushes BI andxB'Z o'f thetransmitterzdistributor :TS :take totraverse 'one Y segment. vvThecommutatonRC .has ttWoi segfrn'entsRSI, RSZ (Fig. l): equallyspacedfandzcon; nected to fa fslip ring *RCR vearthed fat i9; "thebrushes, however, are spaced to give four release pulses foreach halfrevolution :and asfwillf befexplained fully 'with reference toFigurelIl, the -re- -lease pulses for the successive channels are spaced eightmilliseconds apart since each 'channel signal element Aperiod =isSZmilliseconds vas determined by Ythe distributofTS-and each vof thefourchannels has to transmit one of four equally spaced elementsfduring'that period. 'The brush RCA 'o'ffthe distributorv RC 'is adjustableangularlyto permit the time ofrelease 'o'f the A channeltransmitter tobefadjusted relatively to the commutatorSCto enable :the-` selectionsmade bylthelatter to occur 'inthe middle of'le'ach signal unit. Theotherthreebrushes RCB,'RC'C an'dRCD arer adjustable vin 'the same fWay.

-The Wdthof each segment of 'the commutator SC is fsuch that eachpair`of the four pairs of brushes for examplejbrushes 'SCI vandSCA arebridgedby'a segment -for approximately onemillisecond and fin isuch aphase relationship with each -unit 'of 'the lsignals recorded on the'input relayIRA, that the brushes are bridged in the middle of eachsignal'unit. This is illustrated in Figure "4' 'of vWhich lsomepreliminary explanation is necessary. 'The lfour upper traces 2'8, "29,v3i) and 31 show a five-unit signal for a complete characterineach'channel. In the A and Cchannels the-traces 28 and`3ll obviouslyshow a signal which inV the live-unit code vis the let--v ter' Y; v'onthe other hand the traces '29 -an'd 3l exhibit a `character `which`happens "lto be the letter R -i-n the r 5-uriit -code so 'that thesetraces show a completesignal `of the letter'Y on the "A and Cfchannelsand of 'the letter R on 'the B-and'D channels.- These tracesevidentlyshow the signals .as sent out from the input relays'IRA toTIRD. "It iwill ybe followed from vthe above explanation that the`-release pulses sent fto the release lmagnets' IRM in fthe `fourchannelsfoccurrat the-linstants'S.. 33,-i`3 4 :and-135 fvvhi'ch lfollowone amenace f another at intervals of eight milliseconds as alreadymentioned and this is determined by the spacing of the brushes on thedistributor RC. In fact, the brush RCB is spaced 8l degrees from RCA,that is to say, two and a quarter signal units after RCA. The brush RCCis spaced at 193 degrees after RCA which is equal to five and a halfsignal units and brush RCD is spaced 279 degrecs after RCA, that is tosay, seven and three quarter signal units after RCA. Thus, in one half arevolution, the release pulses occur at one quarter signal unitintervals.

VNow the point at'which the brushes SCI and vSCA of the commutator SCare bridged is indicated by the arrows 36 and, as already mentioned,this bridging happens at the middle of each signal. The bridging of thebrushes SC2 and SCB which are allocated to the B channel occurs 8milliseconds later as indicated by the 'arrows 31. Similarly thebridging of the brushes SC3 and SCC again occurs 8 milliseconds later asindicated by the arrows 38 in Figure 4 and iinally the bridging of thebrushes SC4 yand'SCD occurs as indicated by the arrows 3S. The spacingand setting of the brushes SCI, SCA, SC2, SCB to SCD is such as toproduce this timing so that the respective pair of brushes are alwaysbridged at the middle of a signal element in the respective channel. Theinterval between two successive bridgings in one channel as shown inFigure 4 between two successive arrows 3S for example, is of course, 32milliseconds which represents the interval between the centre lines oftwo successive segments of the commutator It will' be seen that thebrushes SCI, SC2, SC3 and SC4 are connected to the conductors I, 2, 3, 4respectively whereas the brushes SCA, SCB, SCC and SCD pass respectivelyto conductors 5, 6, 1 and 8 which pass to the keyers AK to DK of therespective channels. Thus, the function of the commutator SC is so tospeak, to sample each of the live-unit signal elements for a period of lmillisecond approximately at the middle of the element in question andto pass that sample on to the keyer of the respective channel.

The conductor from the brush SCA passes to the right hand grid 44 of adouble triode valve VI the two parts of which are connected as aflip-flop electronic relay. Thus, if the incoming signal unit ispositive, the grid 44-is rendered positive, and the right-hand anode 45becomes conducting and the left hand anode 46 non-conducting whereas thecondition is changed over in the Acase of a negative signal unit. Inother y words, the signal recorded on the input relay IRA is transferredto the valve VI in the denite phase relation indicated above withreference to Figure 4. In the A channel as explained with reference toFigure 4, the grid 44 receives a sample signal every 32 milliseconds sothat the signals on the valve VI have a fundamental element ofmodulation of 31.25 bauds. It will be observed that the left hand anode46 of the valve VI is connected directly to the two anodes of anotherdouble triode V2 whereas the right hand anode 45 of the valve VI isconnected directly to the two anodes of yet another double triode V3 sothat when a positive signal unit is received on the A channel and thevoltage of anode 4S becomes positive, the two anodes 41, 48 of thetriode V2 remain positive until a negative signal unit is received andrenders the anodes negative again. As soon as a negative signal unit isreceived, the anode 45 becomes positive so that the anodes 49, 50 of thevalve V3 then remain positive until another positive signal unit isreceived. This is illustrated in Figure 4 by the traces 5I and 52 whichrepresent respectively the variation in voltage on the anodes 41 and 48and on the anodes 49 and 50 when the signal indicated by the trace 23 isreceived on the A channel. The voltage of the anodes 41 and 43 becornespositive as shown at 5I when the brushes SCI and SCA are bridged and therelay IRA is in the positive position so that this'condition commencesat the middle of the signal unit 28. During the same time, the trace 52is negative and as the negative and positive signal units are receivedin succession, the voltages on the two pairs of anodes, reverse as shownby the traces 5I, 52.

As previously stated, the chopper disc LC 'in terrupts a light beam fromthe lamp L to produce pulses in the photo-electric cell PCI equallyspaced due to the slits I4. There are 32 slits and the disc LC asalready mentioned makes one revolution in 128 milliseconds so that thepulses follow one another at intervals of four milliseconds. Thesepulses occur on either side of the middle'points of the signal units asrepresented by the voltages on the anodes 41, 48 and 49 and 50. Thesepulses for the' A channel are repre# sented in Figure 4 by the arrows53a, 53h where itl can be seen that the pulses occur two millisecondsbefore and two milliseconds after the middle of the signal unitappearing as the voltages on the anodes of the double triode tubes V1and V2. The pulses are fed into the common ring of the commutator PD(Figure 3) so that they are distributed to the chanel keyers for whichpurpose, the brushes PDI to PDS are suitably spaced. Thus, in the Achannel, the brushes PDI and PD2 are connected to the valves V2 and V3,the brush PDI being connected by a conductor 54 to the left hand gridsof both the valves V2 and V3 and the brush PD2 being connected by aconductor 55 to the other grids of those valves. The brushes PD3 to PDBare similarly conected to the keyers BK, CK and DK of the other threechannels in the way shown in Figure 3.

The code conversion is elected by the valves V2 and V3 in the followingmanner. Assuming that the valve VI is receiving a positive signal unitso that the right half of the valve is conclue-V tive, this will place anegative voltage on the anodes 49, 5U of the valve V3 and a positivevoltage on the anodes 41, '48 of the valve V2.

. New the first selecting pulse from the brush PDI arrives on the lefthand grids 56 and 51 of the valves V2 and V3 and consequently the onlypath effective or conductive in these valves V2 and V3 at this moment isthat of the left hand anode 41 of the valve V2. This causes a positivepulse to pass from battery v. through resistance 58, anode 41, cathode59, conductor 6I), diode D6 to the left hand grid 6I of a double triodevalve V4 which is a flip-flop connected valve forming part of the mainoutput relay. This positive pulse represented at 53d in Figure 4 makesthe left hand Vanode 52 of thevalve V4 conducting` which gives themarking condition. The sec-A ond pulse arriving from the brush PD2, asshown at 53o in Figure 4, four milliseconds after the first pulse camefrom the brush PDI applies positive voltage to the right hand grids 63,64 of the valves V2, V3, but as only the valve V2 has positive voltageon its anodes, it is only the right half of the valve V2 which iseiective and its anode. 48.-.conductive 17passes'from battery +120 v.4through theresistthrough the diode Dl to the right hand grid 6'? of thevalve V4 so that this second pulse turns .over the valve V4 to thespacing condition. The

valve V5 inter-connected with the valve V4 is 'providedas an amplifyingstage with its output yappearing across the right-hand cathode resist-:ance .6111.

yThe keyers BincK, and DK in the other three .channels are similar tothose shown at AK and produce similar effects on the valve V4 at the.correct instants so that as the commutatcr PD rotates and engages thebrushes PD! to PDB to .fsupply the .first and second `selecting pulse toItall the keyersin turn, the valve V4 records an `vaggregate oftheconverted signals having a fundamental element of modulation of 4milliseconds or in other words, 250 bauds. .In Figure 4,

:in` .the last four vtraces 68, 69, 'l0 and ll, the

' :transmitted bythe valve V4, and., in fact, is shown in lthe top`trace in Figure 9.

It will-.be understood, of course, that the sys- .temis -in no Waylimited to time division multiplex operation because if it is preferredto Work with-'a lower maximum keying speed, it may be arranged for onlytwo `or even one of the keyers AK to DK. to control the main outputvalve V4. Thiscan be effected, for example, by providing each .o'i thechannels with a main relay such as V4, V5 and using selectingpulsesseparated by four divides; that is to say, for example, by usingthe brush PDS `for the i'lrst `selecting pulse and PD4 for the second,the A channel keyer AK could be operated at single channel speed or Ait.could be operated at the four channel speed as previously described byusing the distribution brushes PDI .and PD2.

Referring now to Figure 5, the signalsfrom .a radio receiver are passedto a main receiving relay RR shown in detailv in Figure 6 and the out-`put'frorn that relay is .connected by conductors 86, 8l to the fourchannel comparators AC, BC, CC and DC. The -main receiving unitlincludes asynchronous electric motor SM2 arranged to .drive in a ixedphase relation .a selecting base light beam chopper disc RLC, aselecting base distribution -commutator DR, a synchronizing base .lightbeam chopper SBC, a synchronizing distributor SD and a channeldistributor synchronizing alternator SRA. This last component isgeared-to the motor SM2 at 'l2 so that an .alternating current of 50cycles per second is generated in the valternator winding '13. .Theother four members .RLC`, DR, SBC `and SD rotate at the same .speed asthe chopper LC in the transmitter shown in Figures l and 3, that isitosay, at 458.75'rev0lutions per minute. Therefore the chopper disc RLCinterrupts the light from a lamp L2, 352 times per revolution, that isto say, once-every four milliseconds. The chopper RLC .also -has vaphoto-cell PC2 similar to the photo-cell P Cl connected throughfanampliner PCA2 so as to apply the selecting pulses to the common ring 14of the commutatorDR. `The amplifier PCAZ is, ingeneraha conventionaltwostage resistance lcapacity coupled-high gain .am-

14 `..plierfshownrin greaterdetail yin :Figure 1,7. Each f-of fthepulses vthus `appliedto .the yring'14 hasf'a fdurati'on" ofapproximately i250 #microseconds Yfiat .a'voltage when connected `to vahigh resistance .load of -faboutf-90 '-to 10.0 vvolts positive. '.The:com- .'-mutator DR fis'fso arranged that'ztheiselecting pulses occurtheoretically iat the imiddlegof each,

`'element of Ymodulation of the aggregate' signa-ls -as Will beexplained more ffully later lin-connec- `tion- With liigure'v 9 Thecommutator DR .clearly passes-` pulses 1in -iturn gto `eight brushes.DRI .to v,DRIV-andtworof -these brushes are connected toeachxofthefchan- -nel fcomparators AC Lto DC. Thus, tthelibrushes l and.'-DR2 are yconnectedito *the vcomparator `AAC =of the fA channel.Each-:brushDRl to DR8 .-is in 'contact-fin fturn with a'commutatorsegment for-approximately two milliseconds V`:and Vactuallyithe path`for any selectingpulse through pne -of Athe segments f0.7, thecommutatorDRiis established before the pulseiis :generated'bythe discRLC yso .that any'slight.irregularityfppn- :tact vwith the brushes idoesnot affect `vthe1 shap of' the vvselecting pulse.

All of .the-components will be Vdescribedzin'de- 'tail flater Abut .it-may be Amentioned that vaca-ch channel comparator :AC to DCaisrconne'ctedto-ia 'channel distributor AD to-Dllfeach of Whchfcomrisesa'multi-vibrator'MVA fedirom :the ;alternator v.Winding 313 Vthrough a.50 'cycle ampliiier 1,5 aand also comprises a150-cy,cle synchronousmotor SMA to SMD. :The-:channel Adistributors AD to LDD :deliverthrough'conduc- 'tors-*iii which :are the 'respective teleprinter'lines..LAS lalready indicated, 'the idisc SBCis:,a"synchro .-fnizing basechopper and .controls a` light 'from' a damp L3 Ato* a furtherphoto-:electric cell'fRCB'and Vthe resulting pulses .are amplified atMandare ypassed to V:a synchronizing panel =SP which icon- .trels a'field VreverserFR fforregulating a direct vcurrent shunt motor 'fl-1a.The motor T'Ia'iis '.gearedj'to` the -'stator '1.8 ofthe synchronousmotor "SM2 rso vas "toturnit in either directionf'to 'cor- `rectthephase ofthe components drivenlby'the' Ymotor 'SM2 .in dependence uponAthe freceived Asignals whichare vpassed Ato the synchronizing panelfSPthrough aconductor 19.

The main receiving relay .RR is'shown in -de- -tail in yFigure 6,Signals fromith'e-.radio receiver inlay :bepassedlto .this lrelay on asingle :wire-for two-wires, as convenient, in vtheforrn-of ydirectcurrent reversals. However, in the presentr'example,the positive signalelements apply positive signals to the conductor and vnegative signalelements apply similar signals'to the conductorl. Therelay RR comprisestwo pentodes P! and P2 which are connected as a dead -beatmultivibrator, the anode .B2 of the valve PI being connected to theinput grid 83' of the va1ve`P2 and thev anode 340i the valve P2 beingconnected to the input grid 85 .of the valve Pl. The anode voltages ofthese valves appearing in the conductors 86, "8l vprovide a two-wiresignal output. Theanodestand 84 are supplied from Aa source +'v.atBB-and it'will be observed that the Acathodesg and Si! are connectedvthrough a resistance SIR to a source -120 v. at 9i so that a full240volt high tension supply is applied torthis relay. The circuit is soarranged that when the incoming .signalis a positive element :applied tothe grid .35 .of the valve Pl, Vthe .latter becomes .conducting and.owing to the reciprocal connection, the'valve 'V2issubstantially.non-conducting. In this condition, theanodervoltage lofthe valve?! falls =,to.-;approxi1nately 'F75 voltsnegative andthat ofthevalve P2 is approximately 100 volts positive. Similarly an incomingnegative element causes the potential of the anode 82 to becomeapproximately 100 volts positive and that of the anode 8l to drop toabout '75 volts negative. Thus the voltage on the conductor 8l is about100 volts positive and that on the conductor 86 about 75 volts negativefor one condition which reverses to set up the other condition ofmodulation of the incoming signals. These signals are, of course, in theform of transit code signals and for the sake of clarity, they are shownin' the top trace 92 in Figure 9. This trace represents the aggregatesignals and by comparison with Figure 4 it will be seen that the sameexample has been taken as for the transmitter, viz. letter Y in the Aand C channels and letter R in the B and D channels. 1n fact it will beseen that the trace 92 is a combination of the traces 68, 89, 'l0 and 1|at the foot of Figure 4; it thus represents the changeltvith time of thevoltages on the conductors 86 and 8l, the high .level of the trace 92representing about 100 volts positive and the low level about 75 voltsnegative. The coupling and breakdown resistances shown inl Fig. 6 areaccording to normal practice and neednot be referred to in detail.

The two wire output 86, 81 of the main relay is connected to all fourchannel comparators AC to DC as seen in Figure and the referencenumerals 86, 87 are applied to the connection in that ligure also.

In Figure '7, the circuit connections of the comparator for one channelare shown in detail. It may be assumed that this is the A channeh Theconductors 86, 81, applying the output of the main relay appear at theleft of Figure 7 and proceed to what may be termed the iirst signalselection section. This section comprises two gate triodes GM and GS anda double triode Rl. These three valves serve as a storage stage. Thedouble triode Ri is connected as a dead beat multivibrator or nip-flopwith two conditions of 'stability and in each of these conditions, one

anode 93 or 94 is approximately at 45 volts negative and the other atapproximately 120 volts positive relatively to earth. Both anodes aresupplied from the +120 v. line 88 and the cathodes are connected to the120 v. line 9i. During the operation, the voltage of the cathodes 95, 96varies between about 55 and 60 volts negative.

The anode 8G of the pentode P2 of the main receiving relay is connectedby conductor 81 to the anode 97 of the gate valve GM so that during allmarking signal elements received in the aggregate signals, the anode 97is at about 110 volts positive; the anode 82 of the pentode P! isconnected by conductor 85 to the anode 99 of the gate valve GS so thatall spacing signal elements of modulation in the aggregate signal areset up as positive voltage on the anode 95. The grids 99, il of thevalves GM and GS are connected respectively through resistances 10i, H32to the rst brush DR! of the ccmmutator DR so that these grids bothreceive what has been called the first selection pulse obtained from thephoto-cell PC2 under control of the chopper disc RLC as described withreference to Figure 5.

In passing, the amplier PCAZ is shown in detail in Figure 7. This hasbeen already referred to but it may now be pointed out that it consistsof a triode AT, resistance-capacity coupled to a pentode AP, the inputto the grid [U3 of the valve AT being derived from the photo-cell PC2which has a source v. applied to its anode and the output from thepentode AP is connected to the brush Iii@ bearing on the common ring 14of the commutator DR. The anodes of the valves AT and AP are suppliedfrom the +120 volt source and their cathodes are connected to the -120v. terminal of the source.

Resuming the operation at the stage at which the rst selection pulsefrom the brush |04 has 'passed through the brush DR! to the grids 99,|00 of thevalves GM and GS, the timing is such that these selectionpulses occur approximately at the middle of each rst signal element andare indicated in Figure 9 by the longer arrows marked l. For the sake ofclearness, the trace 92 has been divided into sections marked with theletters ABCD indicating the time intervals allocated to the differentchannels. The symbols -l-- indicate whether the signal units arepositive or negative in the transit code.

The pulse indicated by the long arrows l maires the grids of both valvesGM and GS positive and renders both valves conductive. It will berecollected, however, that if the signal element received is a markingelement, the anode 91 is positive and the anode 53 is negative. Thiscondition, of course, is represented in Figure 9 by the iirst signalunit in the A channel in trace 92 which is positive in the transit codeso that its first element is marking. Under these conditions, the valveGM conducts and the voltage on its cathode H35 rises to about '75 voltspositive for the duration of the selection pulse. This voltage isapplied to the left-hand grid IE6 of valve RI making its left anode 93conducting which is the condition of the valve Rl corresponding to apositive signal element. At the end of the selection pulse, the voltageof cathode |95 falls to about 40 volts negative leaving, however, thegrid i535 of the valve RI positive relatively to its cathode 95. Nothingfurther happens to the valve RI until the rst element of the next signalbelonging to the A channel is recorded on the main relay and this willoccur with the next first selection pulse on the A channel, in fact, atthe time of the arrow la in Figure 9 which, it will be recollected, is32 milliseconds after the first selection pulse just discussed.

It will be appreciated that under the above conditions, the voltage ofthe cathode |01 of the valve GS is approximately 75 volts negative sothat the right hand grid mi! of valve Rl is negative relatively to itscathode. Consequently, should the next signal on the A channel benegative as it happens to be at the time of the pulse la in Figure 9,the anode 9B of the valve GS is at about volts positive when the rstselection pulse la is applied. Then the nip-nop valve Rl is keyed to itscondition to set up the negative signal element. In Figure 9, this isillustrated in the trace la which shows the resulting signals in the Achannel established at the anodes of the flip-nop valve RI. It will berecognised of course, that the ordinary five-unit signal for the letterY is thus obtained at the receiver and in fact the trace 38a correspondsprecisely to the trace 2S in Figure 4. Three other traces |09, H0, I ll, could be prepared in precisely the same way to show what would occurat the Ri valves in the comparators of the B, C and D channels whenreceiving the signals shown in the trace 92. The long arrows i showingthe rst selection pulses in the successive channels are spaced apart byfour milliseconds as the brushes DRI, DRB and DRS, DRI of succeedingpairs come into play as

